The invention relates to a method and an apparatus for controlling the operation of an internal combustion engine in a predetermined domain. The method and apparatus relate to changes in the fuel-air ratio provided to the engine or the amount of recycled exhaust gas in dependence on the dispersion of the cyclic variations of the mean combustion chamber pressure during intervals which are synchronous with the engine r.p.m. (dynamic stability control). A method and apparatus of this type was described in allowed parent patent application Ser. No. 564,073, now abandonded to which the present application is a continuation-in-part. The method and apparatus of the parent application Ser. No. 564,073 relates to controlling the operational behavior in a predetermined domain near the lean running limit of the engine.
Due to the increasingly rigorous regulations concerning exhaust gas composition and in view of the general fuel shortage, there is the need for methods and means for operating internal combustion engines in a domain wherein the toxic components of the exhaust gas can be reduced to a minimum and/or in which a minimum amount of fuel is used. When an engine is operated near the so-called lean running limit, a relatively innocuous exhaust gas and low fuel consumption may be expected, but the determination of the desired lean running limit is difficult. The sharply fluctuating pressures in the various cylinders of the engine during such operation provide some information regarding the engine operation but in practically useable cases, this pressure can be determined only with difficulty. For this reason, the parent application Ser. No. 564,073 proposes to measure the fluctuation of the mean combustion chamber pressure indirectly by measuring changes in the crankshaft speed or acceleration due to fluctuations in torque and to make this measurement, for example, by measuring the period of rotation between two predetermined angular positions of the crankshaft. The fluctuations of the angular velocity of the crankshaft may be measured by a suitable circuit described in the parent application and may be compared with a set-point value which is itself changeable, depending on r.p.m. and, for example, induction tube pressure, and which relates to a just permissible engine instability in any particular operational domain. A comparison of the actual and set-point values generates an output signal which is preferably fed to an integrating final control element whose output signal may be used to regulate the fuel-air ratio provided to the engine or else to regulate the quantity of recycled exhaust gas.
Yet another engine variable which must be adapted and changed according to the prevailing engine operating conditions is the ignition angle .alpha.. It is known to change the ignition angle of an internal combustion engine based on the changes in vacuum in the induction tube, thereby achieving a desired spark advance. It is also known to change the ignition angle in dependence on the r.p.m. by means of centrifugal governors.
Yet another method for adjusting the ignition timing of the engine is made known by the German Auslegeschrift No. 1,125,230 which describes how one may use another engine variable than the ignition timing, for example, the fuel-air ratio, the degree of compression, or the like, to undergo continuous oscillating changes at a rate which is relatively slow compared with the engine r.p.m. and to use the resultant positive and negative r.p.m. changes of the crankshaft for adjusting the center of oscillations of the controlled engine variable.